child_process: use stdio.fd even if it is 0

Previously, in _validateStdio we were using stdio.fd || stdio. If
stdio.fd was falsy (or 0 in the case of stdin), then the entire stdio
object would be passed which could cause a crash.
Fixes: #2721
PR-URL: #2727
Reviewed-By: silverwind - Roman Reiss <me@silverwind.io>
Reviewed-By: cjihrig - Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: indutny - Fedor Indutny <fedor.indutny@gmail.com>

Author: evanlucas

lib/internal/child_process.js

@@ -713,7 +713,7 @@ function _validateStdio(stdio, sync) {
 }elseif(typeofstdio==='number'||typeofstdio.fd==='number'){
 acc.push({
 type: 'fd',
-fd: stdio.fd||stdio
+fd: typeofstdio==='number' ? stdio : stdio.fd
 });
 }elseif(getHandleWrapType(stdio)||getHandleWrapType(stdio.handle)||
 getHandleWrapType(stdio._handle)){

test/parallel/test-child-process-validate-stdio.js

@@ -28,3 +28,15 @@ var stdio2 = ['ipc', 'ipc', 'ipc'];
 assert.throws(function(){
 _validateStdio(stdio2,true);
 },/YoucannotuseIPCwithsynchronousforks/);
+
+conststdio3=[process.stdin,process.stdout,process.stderr];
+varresult=_validateStdio(stdio3,false);
+assert.deepStrictEqual(result,{
+stdio: [
+{type: 'fd',fd: 0},
+{type: 'fd',fd: 1},
+{type: 'fd',fd: 2}
+],
+ipc: undefined,
+ipcFd: undefined
+});